Field of the Invention
The invention relates to a drive device for a front-loading washing machine having a laundry drum, the laundry drum is mounted overhung on an at least approximately horizontally disposed shaft within a bearing sleeve of a rigid supporting part fitted to a rear wall of a tub, and the laundry drum is directly driven by a flat-type motor which is likewise fitted to the rear wall of the tub.
Such drive devices are disclosed in German Published, Non-prosecuted Patent Applications DE 39 27 426 A1 and DE 43 41 832 A1, wherein the stator of the motor, which is constructed as a commutatorless external-rotor DC motor, is fastened directly on the bearing sleeve of the rigid supporting part. The shaft is mounted in the bearing sleeve and its outer end is connected in a torsionally resistant manner to the rotor of the motor. In that case, the rotor is a so-called external rotor which engages over the stator windings in the form of a pot and carries poles constructed as permanent magnets. In the automatic washing machine according to German Published, Non-prosecuted patent Application DE 43 41 832 A1, the motor is additionally surrounded by an insulating hood which damps noises radiated from the motor directly to the surrounding atmosphere.
The known drive devices encapsulate the stator, which is exposed to considerable temperature loading as a result of Joule heat in its windings, by a rotor configured in the form of a pot (and additionally by the sound-insulating hood in the case of German Published, Non-prosecuted patent Application DE 43 41 832 A1) to such a great extent that any cooling of the motor at all is lost. That is also reinforced primarily by the fact that such a direct-drive motor can scarcely cool itself by the rotating rotor due to its necessarily low intrinsic speeds of rotation. Therefore, in practice the known drive devices can be used only when they are protected against rapid overheating through the use of external cooling.
In addition, the known drive devices cannot be supplied to the washing machine manufacturer's plant as an already fully assembled motor. Their stators and rotors have to be delivered separately and assembled with one another for the first time at the washing machine factory. As a rule, special assembling equipment for completing motor assemblies is not present and is also not desired in a washing machine factory. Therefore, it is probable that the completion of the stator assembly, which is initially to be connected to the tub system, by the external rotor assembly will regularly only take place in an inaccurate manner. Extremely stringent requirements are made of the maintenance of a small air gap between the stator and rotor poles, with the air gap always being of the same size in each specimen, as far as possible. Stringent requirements are also made of the centered mounting, and those requirements cannot be satisfied in the case of the above-mentioned assembly in a washing machine factory. Therefore, in practice the known drive devices can only be used to a very limited extent.